The overall objective of the project is to distinguish and categorize individual cases of acute lymphocytic leukemia (ALL) in order that the most efficacious therapeutic modality may be selected and implemented. The proposed investigation would focus upon terminal deoxynucleotidyl transferase (TdT) patterns in E-positive and E-negative populations of peripheral and bone marrow leukemic cells. The results of our current work have led to the innovation of three experimentally testable hypotheses: (1) TdT determinations at diagnosis of ALL can predict eventual relapse or long-term remission, (2) Sequential TdT determinations during remission can predict imminent relapse and (3) TdT observations at relapse can demonstrate clones of proliferating cells which are resistant to standard forms of induction therapy. Should the proposed study prove any or all of the hypotheses, as our preliminary data suggest, the bases would be established for improved clinical management of the cases of ALL which do not experience long-term remission.